Its all very well to say VFR flight is "see and be seen" BUT its the time you DONT see the other aircraft that is the problem. I have come close 3 times as far as I remember, first was on my solo X/C, flying along scanning the sky and suddenly this old war bird flew past, opposite direction about 200m off to starboard same altitude. I hope he saw me becasue I didn't see him even thought I was being incredibly vigilant [was in a radar shadow as well which didn't help]. Second time was rejoining at Long Beach, another aircraft was joining as well, the controller was screaming at me the traffic info, I couldn't see it at all. The controller was screaming at the other aircraft, and he couldn't see me. In the end the controller gave me vectors and the other aircraft appeared out of a blind spot less than 100m away, and I guess we appeared out of his blind spot. Third time was climbing out of Long Beach again, just departed and picking up VFR flight following, and was issued a traffic alert, traffic less than 0.25 mile, same altitude coming straight for us. We took avoiding action by decending rapidly [he should have turned right] as we didn't feel it safe to turn. The scary thing was that in avoiding this aircraft we flew through the wake of another unseen aircraft which must have been in that spot less than a few minutes before.
In all these experiences we were flying VFR, scanning the sky and not playing with gadgets in the cockpit. These other aircraft just weren't seen, not through lack of trying. Maybe all GA aircraft should be painted a high vis colour or something, or tow a banner with a big arrow pointing towards the aircraft
The scary thing is that in the UK you are perfectly allowed to fly around in cloud [with IMC rating] with no form of radar service at all, and no flight plan,.....sends shivers down my spine ! In fact Radar services are 'discouraged' by a lot of people I've talked to, especially in good weather. I would not dream of flying in the LA Basin without a radar service even in good weather, you would have to be mad or suicidal in my opinion.
Rgds
EA